assume cs:codesg, ds:datasg
datasg segment 
    db 'welcome to masm!'
    db '................'
datasg ends
codesg segment
    start: mov ax, datasg
            mov ds, ax
            mov si, 0
            mov cx, 8
        s: mov ax, [si].0
            mov 16[si], ax
            add si, 2
            loop s

            mov ax, 4c00h
            int 21h

codesg ends
end start